David,

Take the Fluke any day over the HP.

Bill....WB6BNQ

"David C. Partridge" wrote:

David,

The difference between the 335 A or D model I don't recall off the top of my head specifically, but they were improvements.  I
would probably take the D but really either one is good, assuming, of course, they are working.

You might want to consider getting both of them.  They can handle being 1000 volts above ground.  So with two you have a
calibrated DC voltage up to 2000 volts.

You still need a good null meter.  While the 335's null meter is OK, it does not hold a candle to the Fluke 845 when it comes
to isolation.

Are you just gathering this stuff for your own use as a hobbyist or are you intending to get into some commercial concern ?

Bill....WB6BNQ

"David C. Partridge" wrote:

Hobbyist.

The eBay bidding on the Fluke 335D is already going up ...

I still own the 335A (though how long for is another question).

Both the above are spares/repair as is the Efratom FRT (no lock).

The vendor also has Fluke 845 and Fluke 887 and scarily also a 540B, but I can't afford all that lot in one bite :(

I have a Keithley 155 Null Detector how does that rate?

Thanks
Dave
-----Original Message-----
From: volt-nuts-bounces@febo.com [mailto:volt-nuts-bounces@febo.com] On Behalf Of WB6BNQ
Sent: 15 December 2012 02:31
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Fluke 335A versus HP 740B

David,

The difference between the 335 A or D model I don't recall off the top of my head specifically, but they were improvements.  I would probably take the D but really either one is good, assuming, of course, they are working.

You might want to consider getting both of them.  They can handle being 1000 volts above ground.  So with two you have a calibrated DC voltage up to 2000 volts.

You still need a good null meter.  While the 335's null meter is OK, it does not hold a candle to the Fluke 845 when it comes to isolation.

Are you just gathering this stuff for your own use as a hobbyist or are you intending to get into some commercial concern ?

Bill....WB6BNQ

"David C. Partridge" wrote:

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and follow the instructions there.

David,

I had to go research a bit.  The primary difference between the A & D is output accuracy and stability.  Roughly a 2 to 1 improvement.  Keep in mind we are talking splitting hairs.  Either one would exceed what one would
normally need for a small home lab.

As for the Fluke 845, you simply cannot beat it.  If it is not outrageous, grab it.  Hopefully, it is the portable version which had the highest of isolation rating and gives you freedom from ground loops because it runs on
batteries, but the rack mount version is nice as well ( I have both models).

The Fluke 887 is a nice meter as well.  They were very good in their time.  However, a top of the Fluke or HP DVM would give them a run for their money.  If the price is LOW, it wouldn't hurt to have one.  The big draw back is
having to operate all the switches to get a result.  If your constantly operating the switches, they will wear out.  So, it is not what I would consider a general purpose meter, but more of a backup reference standard.  For
normal stuff just use a cheap DVM.

I have all the above equipment except Differential voltmeter is an earlier version, the 883AB, which is the same as the 887 with slightly less accuracy.

Bill....WB6BNQ

"David C. Partridge" wrote:

David wrote:

The three usual suspects are the Fluke 845AB, the HP 419A, and
Keithley 155.  I have one of each, and they are all good meters.  The
received wisdom is that the Fluke is the one to have.  However, in my
view, the Keithley is the best of the bunch.  It is a bonus if you
find one with the rare 1554 AC power module (the 1554 mounts to the
rear panel and allows AC operation -- otherwise, it is battery-only).

The main problem today with the HP is that it uses impossible-to-find
batteries.  Not only are the original batteries unobtainable, I have
yet to find a satisfactory replacement strategy.  It also does not
have a +/- 1 uV range, although I do not count that as a major fault
since thermocouple noise in the measurement setup frequently prevents
taking full advantage of the 1 uV range.

The Fluke's batteries (sub-C NiCd cells) are readily replaced (though
not inexpensively, if you get the best cells).  Keithley used four, #
246 9 V carbon cells, which can easily be replaced with common 9 V
alkalines or 9 V primary lithium cells that simply plug into the
existing connectors.

The HP and Fluke both use photocell choppers.  Fluke published
pre-release information indicating that they had designed a FET
chopper for later production, but I have never seen an 845 with a FET
chopper or a schematic of the FET chopper.  (Does anyone here have
either?)  The Keithley was designed with a MOSFET chopper from the start.

Not only is the Keithley the most modern design and the most likely
to remain reliable, it also performs the best in my lab.  I have had
fewer ground loop and shielding problems with it than with the Fluke,
and it has less noise and less drift.  It is not enough better that
most people should sell their Fluke to get a Keithley just for the
performance difference (reliability may be another story), but -- IME
-- it does perform better.

They are all good meters, but IMO the Keithley is the best of the
three.  If I had only one, that is the one I'd want.

Best regards,

Charles

Hi Charles,
I have a couple of Fluke and HP null voltmeters. One of the Flukes has a FET chopper board in it. It was apparently fitted as part of a repair by Fluke, but I have no data on it. The HP 419 battery packs contain standard sized cells and can be recelled. There are 20 of them so it gets expensive. An alternative is to replace them with a shunt regulator (2 x12Vzener diode) and use mains only. You need the shunt to generate a virtual earth that is provided by the battery center tap in the original design.

Robert G8RPI.

From: Charles P. Steinmetz charles_steinmetz@lavabit.com
To: Discussion of precise voltage measurement volt-nuts@febo.com
Sent: Saturday, 15 December 2012, 10:28
Subject: Re: [volt-nuts] Fluke 335A versus HP 740B

David wrote:

The three usual suspects are the Fluke 845AB, the HP 419A, and Keithley 155.  I have one of each, and they are all good meters.  The received wisdom is that the Fluke is the one to have.  However, in my view, the Keithley is the best of the bunch.  It is a bonus if you find one with the rare 1554 AC power module (the 1554 mounts to the rear panel and allows AC operation -- otherwise, it is battery-only).

The main problem today with the HP is that it uses impossible-to-find batteries.  Not only are the original batteries unobtainable, I have yet to find a satisfactory replacement strategy.  It also does not have a +/- 1 uV range, although I do not count that as a major fault since thermocouple noise in the measurement setup frequently prevents taking full advantage of the 1 uV range.

The Fluke's batteries (sub-C NiCd cells) are readily replaced (though not inexpensively, if you get the best cells).  Keithley used four, # 246 9 V carbon cells, which can easily be replaced with common 9 V alkalines or 9 V primary lithium cells that simply plug into the existing connectors.

The HP and Fluke both use photocell choppers.  Fluke published pre-release information indicating that they had designed a FET chopper for later production, but I have never seen an 845 with a FET chopper or a schematic of the FET chopper.  (Does anyone here have either?)  The Keithley was designed with a MOSFET chopper from the start.

Not only is the Keithley the most modern design and the most likely to remain reliable, it also performs the best in my lab.  I have had fewer ground loop and shielding problems with it than with the Fluke, and it has less noise and less drift.  It is not enough better that most people should sell their Fluke to get a Keithley just for the performance difference (reliability may be another story), but -- IME -- it does perform better.

They are all good meters, but IMO the Keithley is the best of the three.  If I had only one, that is the one I'd want.

Best regards,

Charles

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On 12/15/12 1:28 AM, Charles P. Steinmetz wrote:

Not a 419A expert by any means, but I happen to have 3 I picked up at
parts prices and am repairing the newest of them.

The oldest has a oval 3 pin AC connector.

A newer one has a standard IEC socket.

Both of these have 3 battery packs made of some form of coin cell, NiCd,
225ma, 5 to a stack.

I found some 60ma similar cells in current production (at least in
china), but the right stuff has been impossible to find.

The newest 419 is different.  Different battery holder, and uses 4 packs
of 5 1/3AA cells.  These are not common, but are not that hard to get.

I also found ref in one of the manual change sheets about a different
battery holder.

Now, converting an older unit would not be hard.  The only thing diff is
the mount and the packs themselves.

Take a couple pieces of say 1/2in thick delrin, cut to about 2"x4"
(measure the space).  These mount to the same screw holes as the
original clamp mount.  Cross drill 4 holes for the packs, and stretch a
couple 0-rings around the packs once in.  This is what the newer
mount/pack from the factory is like...  Two flat plates with 4 cross holes.

Anyway, the older coin cell 419s are pretty badly damaged due to leakage
from the packs, am tearing them down for parts.  The newer one didn't
leak, am just shopping for 20 good tabbed 1/3AA cells.  Solder 5, inline
shrinktube, repeat 4 more times and done.